The primary structure of both the catalytic and regulatory subunits of cAMP-dependent protein kinase from porcine muscle are being elucidated. Present efforts are focused on the purification and characterization of the tryptic peptides from the catalytic subunit. At the same time cyanogen bromide peptides from both types of regulatory subunits have been partially purified and are being sequenced. Sequencing is being carried out using the manual dansyl-Edman technique as well as solid-phase sequencing methods. Several types of affinity labeling studies are being pursued. The catalytic subunit has been specifically labeled with p-fluorosulfonyl-(14C)benzoyl-5'-adenosine. The labeled peptide has been purified and is being sequenced. Having so labeled the catalytic subunit we shall now proceed to label the catalytic subunit in the presence of regulatory subunit and characterize the resultant labeled products. The regulatory subunits of both protein kinase I and II have been labeled with the photoaffinity reagent, 8-azido-cAMP. Again a single peptide is labeled and characterization of this peptide is in progress. The sequence around the site of auto phosphorylation on the type II regulatory subunit is also being characterized. The effects of limited proteolysis on the regulatory subunits of protein kinases I and II are being characterized. In particular, the sequences of the AMP-binding fragments generated by proteolysis are being compared.